1. Field of the Invention
The present invention relates to a data readout apparatus and method using optical beams, for regenerating data recorded oil an optical recording medium such as an optical disk.
2. Description of the Related Art
Up to the present, the increase of track density by narrowing the pitch of the track, and the increase of linear density by using a physical format which corresponds to PWM (which uses a pulse-width modulation recording) or MCAV (modified constant angular velocity) have been examined for increasing recording density in optical disks.
Regarding the track density, the track pitch has been narrowed along with the adoption of short wavelength lasers, and a track pitch of approximately 1 micrometer will soon be realized.
On the other hand, the increase of transfer rate for the data read from the optical disk is examined by using multi-beam lasers. For example, as disclosed in, for example, Japanese Patent Application, First Publication, No. Sho 61-17744, plural optical beams output from a multi-beam semiconductor laser are converged by an optical system at plural points on an optical recording medium. Reflected beams from the recording medium are then introduced to optical detectors. The data recorded on the plural points of the recorded medium are regenerated according to the light intensity or the change of direction of the polarization of each reflected beam of the plural optical beams.
However, in the above-described conventional art, regarding the realization of high-density data recording for optical disks, remarkable progress cannot be expected in the future because the development of practical short wavelength lasers is increasingly difficult technically. Moreover, regarding the realization of a high transfer rate of the regenerated data, a practical cost for such an apparatus cannot be easily achieved because in the conventional method, one optical beam can only regenerate one data sequence; thus, a number of regeneration systems corresponding to the number of multi-beams is necessary.